Wire segment pairs are welded to one another in large numbers in a plurality of different application fields. An example of this is the production of three-phase generators for motor vehicles. In this case, it is necessary to weld conductors to one another. In this context, EP 1 850 463 discloses a method for producing weld connections on conductors of a three-phase generator for motor vehicles. The stator of the generator includes in this case a winding embodied from individual winding rods that are pre-bent in the form of a hair pin and are inserted with a forcing-apart step by a pole pitch into the laminated core grooves of the stator. The free ends of the winding rods are interlaced against one another on the other side of the laminated core and are welded in pairs to one another. In the conventional arrangement of insert windings for generators of motor vehicles, the weld connections of conductor segments that are pre-bent in the form of a hair pin lie on one side in the winding head, preferably on the drive side of the machine. However, when by means of individual rods for the conductor segments, it is also possible in the same manner to produce weld connections in both winding heads on both end faces of the stator.
In EP 1 850 463, the winding heads are welded by means of a resistance welding method. For resistance welding on winding heads, material resistance and contact resistance are particularly important. While the material resistance at the beginning of the welding procedure is low and the contact resistances, in the case of copper in particular between the electrode and joining parts, are high, this behavior changes even after a short period of time. As a result, the greatest electrical resistance is not experienced in the joining gap but rather at the contact surfaces between the electrode and the workpiece. Thus, the surface state and the heat conductibility of the conductor segments and electrodes have a great influence on the resistance welding and the quality of the joining process since, for example, oxide layers impair the current through-flow and excessively high heat dissipation losses hamper the joining process.
Therefore, the method disclosed in EP 1 850 463 has the disadvantage of not being able to ensure the quality of the joining process, the disadvantage of only being able to guarantee the automation of the joining process to a low level and the disadvantage of causing damage to the insulation on the winding such as, by way of example, peeling, rupturing or crack formation as a result of high heat dissipation during the welding procedure.